CHEM 1312H 1st Edition Exam 4 Study Guide Lectures 31 37 Lecture 31 4 1 Key concepts solubility ICE tables Ksp Common Ion Effect Review how to do ICE tables and how the addition of a common ion effects the solubility product constant and the reaction Lecture 32 4 3 To recap the the rest of Ch 17 on solubility 17 4 SOLUBILITY PRODUCT CONSTANT The Solubility Product Constant Ksp a saturated solution is one in which the solution is in contact with un dissolved solute o the extent to which the dissolution reaction occurs is expressed by the magnitude of the equilibrium constant which expresses how soluble a solid is in water o Ksp writing rules are the same for Kc rules products over reactants no solids etc o if Ksp is small only a small amount of the solid dissolves in water at a certain temperature Solubility and Ksp solubility the quantity that dissolves to form a saturated solution typically g L o solubility of a substance changes considerably in response to a number of factors pH of solution concentrations of other ions in a solution especially common ions Ksp the equilibrium constant for the equilibrium between an ionic solid and its saturated solution no units o Ksp is one set value for a given solute at any one temperature 17 5 FACTORS THAT AFFECT SOLUBILITY 1 Presence of a Common Ion If you have CaF2 s Ca2 aq 2F aq the presence of either Ca2 or F will shift the equilib concentrations to the left and reduce the overall solubility of CaF2 2 pH The solubility of any ionic compound that contains a basic anion the anion of a weak acid increases as the solution becomes more acidic as more H is present For instance Mg OH 2 s becomes a lot more soluble as the acidity of the solution increases 3 Formation of Complex Ions These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute For example AgCl s solubility is increased in the presence of NH 3 because NH3 is a Lewis base which attracts the Ag ions that form after AgCl dissolves The presence of NH 3 drives the dissolution of AgCl to the right In order for a Lewis base to increase the solubility of a metal salt the base must be able to interact more strongly with the metal ion than water can Something like Ag NH3 2 is a complex ion which are very soluble in water The equilibrium constant for the formation of a complex ion is called Kf and its magnitude tells us the stability of the complex ion in aqueous solution Other common Lewis bases that increase metal salt solubility are CN and OH Amphoterism o amphoteric oxides and hydroxides are soluble in strong acids and bases because they re capable of behaving as either an acid or base themselves o examples Al3 Cr3 Zn2 Sn2 o metal hydroxides such as Ca OH 2 and Fe OH 3 can dissolve in acidic solution but can t react with excess base and therefore aren t amphoteric 17 6 PRECIPITATION AND SEPARATION OF IONS How can we predict whether a precipitate will form under various conditions o Q is the reaction quotient that can determine the direction in which a rxn will proceed to reach equilibrium if Q Ksp the system is at equilibrium the solution is saturated if Q Ksp the reaction will proceed to the right towards the soluble ions no preciipate will form if Q Ksp the reaction will shift left and a precipitate will form Selective Precipitation of Ions when ions are separated from each other based on the solubilites of their salts o for ex if a solution has both Ag and Cu2 adding HCl to the solution will cause AgCl to precipitate will Cu2 will remain in the solution because CuCl2 is still soluble 17 7 QUALITATIVE ANALYSIS FOR METALLIC ELEMENTS Qualitative analysis determines the presence of absence of a particular metal ion relative to some threshold Quantitative analysis determines how much of a given substance is present both proceed in three stages o the ions are separated into broad groups based on solubility properties o the ions in each group are separated by selectively dissolving members in the group o the ions are identified by the conductance of specific tests Lecture 33 4 6 Key concepts solutions properties of solutions entropy Solution a homogenous mixture of 2 or more pure substances in which no separation occurs heterogenous is a slurry sand in water etc Solute the substance that dissolves Solvent the medium in which the solute dissolves Energy that occurs solute solvent solution if the change in energy is negative then the reaction is exothermic products are more stable than reactancts if the change in energy is positive then the reaction is endothermic reactants are more stable NATURE FAVOURS EXOTHERMIC REACTIONS Entropy a natural tendency of substances ot mix and spread into larger volumes when no restrained in some way Lecture 34 4 6 Key concepts colligative properties factors of solubility Henry s Law Raoult s Law molality Ex 1 Compare cyclohexane C6H14 which is insoluble in H2O and glucose C6H12O6 which is very soluble in water glucose has Hydrogen bonding cyclohexane only interacts with H2O via LDF in order to dissolve something we need energy to break apart bonds and we don t have enough because of poor energy Henry s Law Cgas kPgas where C is the solubility of gas in solvent k is Henry s Law constant and Pgas is the partial pressure above liquid Colligative Properties depend on the number of solute particles not the kind of identity compared to pure solvents solutions exhibit vapor pressure boiling point elevation freezing point depression osmotic pressure Lecture 35 4 10 Key concepts osmotic pressure colligative properties Ex 1 You have four identical empty flasks Into flasks A and B you add a small quantity of distilled water Into flask C you add the same volume of seawater Flask D you fill nearly completely with distilled water You then place stoppers on the tops of all the flasks and you leave all the flasks at room temperature except for flask B which you place at a cooler temperature After a shorter period of time you measure the vapor pressure of all four flasks Which would you predict to have the higher vapor pressure A or B A or C A or D Explain A B because A has the higher temperature A C because A is a pure solvent vs C which is a solution A B Tf i Kf m where Tf is Tf solvent Tf solution i number of particles Kf freezing point depression constant m molality Ex 2 0 500 grams of an unknown non electrolyte i 1 dissolved in 15 0 g of C6H6 benzene and Tf 2 06 Celsius Determine